McDonnell Aircraft's F3H Demon was the firm's first swept-wing jet fighter. The aircraft was conceived in 1949 as the XF3H-1, with the first flight taking place in 1951. Unfortunately, the original Westinghouse J40 engine was extremely unreliable, leading to the loss of several aircraft and pilots. Despite the faulty powerplant, McDonnell set an unofficial time-to-climb record in 1955 of 10,000 feet in 71 seconds in an F3H-1N. In 1953, the Demon was refitted with the more powerful and reliable Allison J71 engine. This powerplant substantially boosted the planeís performance. In 1956, the F3H-2N Demon was approved as a front line fighter with the U.S. Navy. In service, the Demon performed well, although it was still somewhat underpowered. However, it was a sturdy, stable platform under all flying conditions. The last of 522 Demons were delivered in 1959 and were not retired until 1964.